#include <fstream>

using namespace std;
ifstream cin("oo.in");
ofstream cout("oo.out");
#define NMX 100005
int n,oo[NMX],dp[NMX],ans;
void dyn_prog(int low,int hi)
{
    dp[low]=0;
    dp[low+1]=oo[low]+oo[low+1];
    for(int i=low+2;i<=hi;i++)
    {
        dp[i]=max(dp[i-1],dp[i-3]+oo[i]+oo[i-1]);
    }
   ans=max(ans,dp[hi]);
}
int main()
{
    cin>>n;
    for(int i=1;i<=n;i++)
    cin>>oo[i];
    dp[n+1]=oo[1];
    dyn_prog(1,n-1);
    dyn_prog(2,n);
    dyn_prog(3,n+1);
    cout<<ans;
    return 0;
}